Low-carb or low-fat? New study finds surprising results

According to a new study, the answer may well be d) any of the above. The report published in JAMA compared diet plans like South Beach, Atkins and Weight Watchers and found that all the programs were about equally effective.

Low-carb and low-fat diets resulted in the most weight loss, but the difference was small, Dr. Bradley Johnston of McMaster University in Ontario and his colleagues found.

“The differences between diet classes (low carb, low fat, moderate macronutrient composition) and branded diet programs is minimal and not likely important to those wishing to begin a diet,” Johnston told TODAY in an email.

The authors say their findings support choosing a diet plan you can stick with, whatever that plan may be. Johnston suggests a structured diet with exercise and behavioral support.

"The recent study in Annals of Internal Medicine is an example of a finding from a single study. Ours is a synthesis of all available data," Johnston said. "Health care decision making should primarily rely on the totality of evidence (i.e., evidence synthesis), not single studies."

In the new study, researchers looked at 49 randomized trials that tested 11 popular, branded diets for at least three months. All the participants were overweight or obese and the diets included low-carb, like Atkins and South Beach, low-fat, which requires participants to restrict fat to less than 20 percent of their calories, and what the authors called “moderate macronutrients,” which included popular plans like Weight Watchers, Jenny Craig and Nutrisystem.

Compared to no diet at all, each of the diets was successful. After one year, people on the low-carb and low-fat diets had lost 16 pounds, while those who moderated macronutrients lost 12.5. The different diet brands within the categories didn’t make much difference.

Johnston said his study didn't look specifically at calorie intake, which he called a limitation.

TODAY diet and nutrition editor Madelyn Fernstrom says the new findings support what health experts have always recommended: “It’s the calories in and calories out that matters.”

If you choose to go low-carb, she suggests thinking about “smart carbs” – eliminating processed starches, sugars and refined flour, and choosing fruits and vegetables as the main source of carbohydrates.

"The good news is that whatever plan ‘speaks’ to you is one that will work for the long haul,” Fernstrom says. "It's all about a plan you can stick with for the long term. That's why it's called a LIFEstyle."